1. Field of the Invention
This invention relates to power transmission belts and, more particularly, to a belt with longitudinally extending, laterally spaced ribs and discrete, laterally directed reinforcing fibers in both the tension and compression sections of the belt in which a) cracking between adjacent ribs is minimized without significantly altering the flexibility of the belt and b) a high friction drive surface is provided on the back/outside surface of the belt.
2. Background Art
Power transmission belts having a plurality of laterally spaced, longitudinally extending, V-shaped ribs have a wide range of applications in many diverse fields. These belts, commonly referred as V-ribbed belts, are used, for example, in the automotive industry, on agricultural implements, on domestic electrical implements, and further on general purpose equipment.
V-ribbed belts have a number of desirable features. Because the V-ribbed belt is normally thinner than a conventional V-belt, it is highly flexible and thus capable of wrapping around pulleys of relatively small diameter. V-ribbed belts are commonly used in what are known as serpentine drive systems on automobile engines. The belt is wrapped in a circuitous path so that engine components are driven by both the inside and outside surfaces of the V-ribbed belt. The flexibility of the belt allows the various components driven thereby to be compactly situated. This is particularly desirable in an automobile engine compartment in which space is at a premium.
The V-ribbed belt is also desirable for its energy saving capability. This is due in part to the highly flexible nature of the V-ribbed belt.
A still further advantage of the V-ribbed belt is that the individual ribs do not penetrate the grooves in a cooperating pulley as deeply as those in a conventional V-belt drive system. By minimizing the friction between the belt and pulley as the belt engages and disengages from the pulley, abrasive wear on the belt is reduced over conventional V-belts. Further, less tension is required to be applied to the belt during operation. The advantages of this are both a savings in energy during operation and prolongation of the belt life.
All of the above features make the V-ribbed belt desirable in the wide range of industries in which it is currently being used.
The V-ribbed belt, however, does have a number of drawbacks. One problem is encountered with the V-ribbed belt in a serpentine drive system in which both the inside and outside surfaces of the belt are used for driving purposes. The outside surface of the belt, which is typically flat, i.e. without ribs, facially engages an annular surface on a pulley to be driven by the belt. To reinforce the outside surface of the belt, typically the exposed outer surface is defined by a rubber-coated fabric. However, the fabric, while reinforcing the outside of the belt, reduces the coefficient of friction on the outside belt driving surface and results in the belt slipping relative to the pulley, which thereby reduces the power transmission capability of the back/outside surface of the belt.
One solution to this problem is to define the exposed outer surface by a rubber layer. This improves the power transmission capability of the back/outside surface of the belt. However, the unreinforced outside rubber layer is prone to cracking, particularly where it laterally coincides with the troughs between adjacent ribs, where the belt is the thinnest. A crack that originates in the rubber layer may propagate freely. There is a resulting tendency of the ribs to break away from each other at the relatively thin portion of the belt between ribs.
In addition to the above problems noted for V-ribbed belts using a rubber-coated fabric in the back/outside surface thereof, such belts further require multiple components, which adds to the cost of manufacture. For example, a conventional belt made according to the above may require four different components: 1) rubber coated fabric; 2) load-carrying cords; 3) reinforcing fibers for the compression section; and 4) at least one rubber composition for the tension section, compression section and load-carrying section defining the neutral belt axis.
There is yet another problem resulting from the use of a rubber-coated fabric on the back/outside surface of the belt. The rubber-coated fabric requires the formation of a joint to produce an endless band from the rubber-coated fabric. In addition to the difficulty in producing a high integrity joint, the joint itself may produce a localized variation in the belt thickness. This variation may induce vibrations to the system and/or may result in inconsistent drive characteristics. Further, the belt is prone to failure at the joint, which could make the belt unusable.